From German Patent Application (DE) No. 40 28 892 A1 a drive mechanism has become known which in particular is used for windscreen wipers of automotive vehicles and which has a shaft projecting out of one front side of a bearing casing, with a cylindrical slide bearing being mounted to the bearing casing with a small spacing in respect of the latter's front side. Because of the slide bearing, an annular gap is confined between the bearing casing and the shaft. A bushing made of elastic plastic is provided for sealing the annular gap with regard to its surroundings. This bushing is fixed on the bearing casing and shuts the annular gap off from the slide bearing. On its end averted from the bearing casing, the bushing is provided with a radially inward projecting sealing flange engaging an annular groove of the shaft. Such a shaft bearing has the advantage of being extremely sturdy. However, the design and assembly of the shaft bearing is complicated and expensive and, as a rule, several components will be required to render the best support and sealing possible.
It is thus an object of this invention to provide a system for allowing the shaft to be easily supported in the bearing casing.
Regarding the method referred to at the beginning, this object is solved according to this invention in that, after insertion and alignment of the shaft in its bearing casing, the annular gap is at least sectionally filled by the injection of plastified plastic material or metal.
The present invention includes embodiments where the annular gap is filled by the injection of plastic material. However, it can also be filled by the injection of a copper, lead and/or tin alloy. Thus, in the inventive method, neither slide or roller bearings are inserted between the shaft and the bearing casing. All that is done there is to fill the annular space by injecting plastic material. After curing of the plastic material the same serves both as a bearing of the shaft and as a seal against the penetration of dirt and humidity from the surroundings into the bearing and/or against leakage of lubricant out of the bearing. This renders the advantage of not having to insert any additional components other than the plastic material into the annular gap in order to support and seal the shaft. Further, manufacture of such a type of shaft fixation is easily and quickly implemented. Admittedly, as a rule, the shaft is aligned, i.e. centered, after its insertion into the bearing casing. This operation, however, is not necessary by all means. Due to the injected plastic material it is also possible to fixate the shaft in offset or tilted positions in the bearing casing. A further advantage of the injection of plastic material into the annular gap is that the internal shape of the bearing casing may also feature a conical design. This is of special advantage in case of cast casings.
Further, there is no need for aftertreating the internal shape after the manufacture of the bearing casing, in particular so with regard to widening it to predetermined dimensions. In particular, no mechanical aftertreatment is required in case of bearing casings made from aluminum die-castings despite the considerable dimensional tolerances caused by the cooling of the bearing casings.
In order to maintain a defined play between the shaft and the cured plastic material the shaft is heated before filling the annular gap by injection, in particular up to a temperature of 200.degree. C..+-.30.degree. C. As, after the injection, curing of the plastic material will take place at a faster rate than cooling of the shaft, a defined play will be generated by the amount of shrinkage of the shaft, thereby an easy-motion rotatability of the shaft is guaranteed.
The plastic material is advantageously injected axially and/or radially into the annular gap. Depending on the shape and accessibility of the annular gap as well as on the gap length and on the temperature of the materials confining the annular gap as well as on the plastic material used the same is injected into the annular gap either radially so that it is pressed to both sides or injection will be axial. Axial injection will be of particular advantage if the bearing casing is not readily accessible from the outside.
In a further embodiment it is provided to inject different plastic materials into the annular gap at the same time or one after the other. In doing so, it is possible to use suitable materials, for instance, with regard to a low friction coefficient, a good sealing action, a high-degree resistance against certain substances such as greases, oils, water or aggressive agents. By way of suitable feed openings, these materials may be injected into the annular gap in succession or simultaneously. In this way, it is possible to combine the properties of the different plastic materials.
In order to prevent the plastic material injected into the annular gap from emerging from the same, the annular gap will be closed axially during the injection, for instance, by means of a tool. This tool advantageously allows the material emerging from the annular gap to be diverted so that this material at least partially is injection-moulded around the axial end of the bearing casing. This will anchor the plastic material on the bearing casing and prevent axial slip.
Fixation of the plastic material in the circumferential direction on the bearing casing is achieved in that the plastic material is injected into recesses provided on the inside of the bearing casing. These recesses can also have undercuts and, in particular, are designed like dovetails. Axial fixation of the shaft is achieved in that the plastic material is injected into recesses provided on the circumferential surface of the shaft. These recesses may be cylindrical or spherical grooves. Other shapes are possible as long as, in the circumferential direction, they are symmetrical with respect to rotation.
According to this invention, the above-defined object is solved in a wiper installation of the type referred to in that the annular gap between the shaft and its casing is at least sectionally filled by the injection of a plastic material or metal.
Thereby, the abovementioned advantages will be achieved. In the following reference will be made to the plastic material injection, with the injection of metal being applicable with the same advantages.
It is possible to reduce the friction between the shaft and the plastic material advantageously in that the plastic material contains the addition of a lubricant. Such additions may be metallic or liquid additions.
With preference, the plastic material is the thermoplastic or duroplastic type. With a thermoplastic material being used, the same will be plastified upon heating and will be injected into the annular gap. Auxiliary tools will fixate the wiper shaft in respect of the bearing casing until the injected thermoplastic material will have cooled and cured. When using duroplastic material the same will be activated, for instance, by means of the addition of a hardener and will be injected in plastic condition into the annular gap. The duroplastic material will set in particular by means of the application of heat and will fixate the shaft. Heat may be applied to the duroplastic material by a heated shaft, for instance.
When cured, the injected plastic material will advantageously provide a bearing and sealing of the shaft. As already mentioned, no further components will be required for the bearing and sealing functions.
With preference, the shaft or the inside of the bearing casing are provided with steps, recesses, shoulders or the like filled by the injection of plastic material. These changes in the shape of the shaft and/or of the inside of the bearing casing provide anchoring points for the plastic material so that, on the one hand, the same is firmly connected to the bearing casing and, on the other hand, the shaft is axially held rigidly by the plastic material.
Axial anchoring of the plastic material within the bearing casing will further be achieved in that the plastic material rises axially and, in particular, radially above the bearing casing. Using a suitable tool, it is further possible to press the plastic material in the area where it axially rises above the bearing casing onto the shaft surface during the curing process. This will render a particularly good sealing effect. At its axial ends, the plastic material on the shaft will taper.
Another way of achieving an optimum sealing action may be that within the plastic material additional seals such as O-rings or the like are integrated. In this case, it is possible to use as plastic material, for instance, a material designed for an optimum sliding friction coefficient, an optimum sealing action being achieved for instance by the O-ring injected, i.e., integrated into the plastic material. In this way it is possible to combine the properties of the O-ring with those of the plastic material.
A further sealing type as well as a better type of anchoring of the plastic material will be achieved in that the bearing casing has a circumferential axial groove provided on its axial ends. The plastic material can be injected into this circumferential axial groove or, as long as the axially emerging plastic material is still plastically ductile, it can be pressed into the circumferential axial groove.
In some embodiments, the shaft is provided to be the driven shaft of a wiper motor. In another embodiment the shaft is that of a wiper bearing. In the first-mentioned embodiments, the bearing casing is the casing of the wiper motor or rather of its gear and in the second-mentioned embodiment of the wiper bearing the bearing casing is formed by the bearing bush receiving the shaft.